Optical recording medium and manufacturing method thereof

ABSTRACT

An optical recording medium according to the present invention includes a data recording area forming a double spiral structured track having spiral recording tracks each formed of a groove and a land adjacent to the groove, and a reproduction only area forming a single spiral structured track consisting of a pit row.

BACKGROUND

1. Field of the Invention

The present invention relates to an optical recording medium,particularly to one aiming for improvement and the like of recordingdensity of a write-once or a rewritable type optical recording mediumalso having a reproduction-only recording area.

2. Background of the Invention

An optical disk which is one kind of the optical recording mediumgenerally has a spiral shaped track at a predetermined pitch p (forexample, p=0.7 to 1.6 μm) in a signal recording area 2 on one surface (asignal surface) 4 of a substrate 3 made of optically transparent plasticas shown in FIG. 1A. The track consists of either continuous grooveshaped concaves and convexes (groove 5 as a concave portion and land 6as a convex portion) as shown in FIG. 1B or a pit row formed ofcontinuous pits 8 as shown in FIG. 1C.

Of the optical disks, in an optical disk which makes it possible for auser to write in information (hereafter, referred to as a recordableoptical disk) such as a write-once type and a rewritable type employinga phase change recording method or a magneto-optical recording method,what constitutes the main current is one which employs either the groove5 or the land 6 in FIG. 1B as a recording area while employing theremaining one as a tracking light reflection area.

On the other hand, in the reproduction-only optical disk, whatconstitutes the main current is one in which the pit row where the pit 8is continuous in FIG. 1C is employed simultaneously as a recording areaand a tracking diffraction grating.

When information is to be recorded and reproduced, a laser light isirradiated from an optical pick-up (not shown) upon an opposite surface(read-out surface) 7 of the signal surface 4 while an optical disk 1 isrotated by the driving of a spindle motor (not shown).

Then, in a recordable optical disk, at a time of recording, informationis written by its irradiating light in, for example, a record area onthe land 6 as a mark which is equivalent to a pit in thereproduction-only disk, and at a time of reproducing, the writteninformation is read out by a reflection light. Also, in order that thelaser light for the recording and the reproduction is always irradiatedon a predetermined track, tracking is carried out by detecting, forexample, a reflecting light from the grooves 5 and the lands 6.

On the other hand, in the reproduction-only optical disk, read-out ofthe information and the tracking are respectively carried out bydetecting a reflecting light and a diffraction light from the signalsurface 4 on which the pit row 8 is formed.

Since the shape of such the track affects performance as a recordingmedium, it is demanded that the substrate 3 is most preciselymanufactured. FIG. 2 illustrates a generally practiced manufacturingprocess of the substrate of an optical disk.

(1) Manufacture of a master

Glass as a material for a master is worked to become a plate shape, itssurface is ground sufficiently flat, washed and dried whereby a glassmaster 23 is manufactured.

(2) Painting of photoresist

Photoresist, e.g., positive type resist which becomes soluble in alkaliby exposure treatment 20 is painted about as thick as about 0.1 μm onthe glass master 23 and the photoresist 20 is dried by carrying out heattreatment on the glass master 23.

(3) Recording by a laser beam (cutting)

The photoresist 20 is exposed to light by condensing a recording laserlight 31 by an objective lens 32 and irradiating it on the photoresist20 on the glass master 23. In a case of the recordable optical disk, theirradiation is carried out continuously and in a case of thereproduction-only optical disk, the irradiation is carried outintermittently. Concurrently, an exposure spot is fed in a radiusdirection of the master 23 at a constant feeding pitch, i.e., at anequal distance per one rotation while rotating the glass master 23 in acircumferential direction. As a result, in the case of the recordableoptical disk, a latent image for a track consisting of a groove in aspiral shape at a constant interval is generated in the photoresist 20whereas in the case of the reproduction-only optical disk, a latentimage for a track consisting of spiral shaped pit rows at a constantinterval is generated in the photoresist 20.

(4) Development

By developing the photoresist 20 in an alkaline developing solution, itsexposure portion is removed. As a result, in the case of the recordableoptical disk, a track pattern consisting of an alternation of a groove25 and a land 26 in a spiral shape at a predetermined pitch is formed onthe glass master 23. Also, in the reproduction-only optical disk, atrack pattern consisting of continuous spiral shape pit rows 28 at apredetermined pitch is formed.

(5) Manufacture of a stamper

By electroforming nickel on the glass master 23 and peeling off a formednickel layer, a nickel master (stamper) 34 onto which the pattern on theglass master 23 is transferred is manufactured.

(6) Plastic molding

By molding plastic as a material for the substrate of the optical diskthrough an injection molding method or the like using the stamper 34, anoptical disk substrate 3 having the track consisting of the groove andthe land or the pit row as shown in FIGS. 1A to 1C is manufactured. Thissubstrate 3 is a replica of the glass master 23.

After the replica is manufactured, a recording film, a reflection filmand the like (not shown) are formed on the signal surface 4 of thesubstrate 3 in the recordable optical disk, while in thereproduction-only optical disk, a reflecting film, a protection film andthe like (not shown) are formed on the signal surface 4 of the substrate3.

FIG. 3 shows a schema of whole the structure of an apparatus (a cuttingmachine) used for carrying out the cutting in the process in FIG. 2, andFIG. 4 shows detailed structure of its optical system. The cuttingmachine is formed of the following parts.

(1) Laser apparatus 41 as a light source

As one example, a Kr ion laser apparatus with a wavelength of 4 1 3 nmis used.

(2) Recording light intensity control unit 42

An apparatus for eliminating instability of output from the light sourceto control the final recording light intensity for which a servo systememploying an electro-optical crystal element (EO) 42 a, an analyzer 42b,a photo-diode 42c, a recording light intensity control circuit 42d isused.

(3) Light modulating unit 4 3

This is an optical system provided with a light modulator 43 a on anoptical path formed of beam splitters BS1, BS2, and convex lenses L1 andL2. The light modulator 43 a is used to form a pit of a lengthcorresponding to a voltage level of an electric record signal, and toconvert the voltage level of the record signal to a light intensity. Forexample, when the voltage level of the record signal consists of 2values such as "0" and "1", a passing light is made on and off. As thelight modulator is required to have performance capable of being used ina band of several tens of MHz, usually, an EOM (electro-optic crystalelement modulator) and an AOM (acousto-optic crystal element modulator)are used.

(4) Beam expander unit 44

This is an optical system to expand a diameter of a beam of a recordinglaser light and a spot diameter of a condensed light is adjusted by itsenlargement factor (magnification).

(5) Objective lens 45

This is an optical system which condenses and irradiates the recordinglaser beam upon the photoresist 20 on the glass master 23.

(6) A turntable 46 for holding and rotating the glass master 23 in acircumferential direction.

(7) Feeding mechanism (not shown)

This is a mechanism for feeding an exposure spot of the record laserbeam in a radius direction of the glass master 23 by holding the beamexpander unit 44 and the objective lens 45 on a shifting stationaryplate and shifting the shifting stationary plate by a motor and the likein a radius direction of the master 23.

(8) Servo system

This is for maintaining a distance between the master 23 and theobjective lens 45 constant in a direction perpendicular to the surfaceof the glass master 2 3, and usually, a focusing laser 47 with awavelength to which the photoresist is not photosensitive 20 is used.

With the use of a cutting machine having such a construction, the latentimage of a spiral groove (or a pit row) at a constant interval is, asmentioned before, generated on the photoresist 20 by feeding theexposure spot of the record laser beam at a predetermined feeding pitchin the radius direction of the master 23 while rotating the glass master23.

An fundamental construction of the optical system in the cutting machineis illustrated in FIG. 3 and FIG. 4, but in a case of the recordableoptical disk, it is necessary at a stage of a manufacturing process ofthe substrate to beforehand record an address signal and the like whichwill become a marker when a user writes information. As a method forthat, there are provided such a method by which exposure for a pit ofthe address signal is carried out at a position other than the opticalsystem for the exposure spot for the groove, and another method by whicha latent image for a serpentine groove is generated by vibrating(wobbling) the exposure spot for the groove in a radius direction of themaster and an optical system corresponding to them is added to thecutting machine.

FIG. 5 shows a schema of construction of a cutting machine having atwo-beam optical system corresponding to the wobbling. There is providedanother optical system (referred to as channel Ch-B) other than theoptical system (referred to as channel Ch-A) shown in FIG. 3 and FIG. 4,wherein the quantity of light given to the Ch-A almost equals thequantity of light given to the Ch-B by setting the transmittance of abeam splitter BS1 in a latter stage of the analyzer 42b to about 50%.However, the transmittance of the beam splitter--BS1 can be set to otherthan 50% corresponding to a necessary quantity of light for each of thechannels.

The Ch-B has entirely the same construction as the light modulating unit43 in the Ch-A as far as the light modulating unit is concerned, and bymaking an electric recording signal supplied to the light modulator 43 ain the (Ch-A) and an electric recording signal supplied to the modulator43a' in the Ch-B different, recording laser lights corresponding todifferent patterns (for example, the group in the Ch -A, the pit in theCh-B) can be obtained.

On the optical path in the Ch-B, is provided a light deflector 51 suchas an AOD (acousto-optical deflector) and the like, and depending on anelectric signal inputted to the light deflector 51, the optical axisdirection of the recording laser light in a direction of a light axisslightly oscillates within one plane. As a result, the exposure spotoscillates on the glass master 23. Further, according to a presentformat of an optical disk, as the wobbling is supposed to be carried outin a radius direction of the master, the light deflector 51 is sodisposed that the exposure spot oscillates in a radius direction of themaster 23 as shown in FIG. 6.

The optical axis of the recording laser light in the Ch-B is alignedwith that of the recording laser light in the Ch-A by a polarizing beamsplitter PBS through a light splitter BS3. Here, as a laser light isemitted from the laser apparatus 41 in a state of a linearly polarizedbeam, the recording laser lights at both channels before the polarizedbeam splitter PBS become the linearly polarized light of the samedirection. As the polarized beam splitter let pass a linearly polarizedlight of a certain direction 100% but reflects the linearly polarizedbeam perpendicular to that direction 100%, in order for the recordinglaser lights at both the channels to reach the glass master 23 withmaximum quantity of light, the linearly polarized light of one channelis sufficient to be rotated by 90 degrees.

Then, for example, in the Ch-A, half-wave plate 52 is provided at afront station of the polarized light splitter PBS, and the polarizedlight splitter PBS lets pass 100% the recording laser light in the Ch-A,wherein the direction of the linearly polarized light is rotated by 90degrees by the half-wave plate 52, and makes the same incident on thelight expander unit 44 while the linearly polarized light splitter PBSreflects the recording laser light in the Ch-B 100% and makes the sameincident on the light expander unit 44.

Also, as the half-wave plate rotates direction of the linearly polarizedlight which is incident thereon at an incident angle of θ relative to adirection of a crystallographic axis within the plate surface by angleof 2θ, if the incidence angle of the recording laser light in the Ch-Aon half-wave plate 52 is adjusted to change a rotating angle in adirection of the linearly polarized light, because the transmittance ofthe recording laser light in the Ch-A in the polarized light splitterPBS varies from 0% to 100% a ratio between the quantities of light ofthe recording laser lights in both the channels can finally be adjusted.

The recording laser lights in both the channels, which have passedthrough the light expander unit 44 are condensed by the objective lens45 and subjects the photoresist 20 on the glass master 23 to theexposure. The exposure spots of both the channels are spaced apart by aminute distance in a radius direction of the glass master 23 (generallywithin one half a pitch of the track, that is, as much as about 1 μm atthe maximum). An adjustment to the end is carried out by giving thepolarized light splitter PBS "a swing angle" so that a reflection angleof the recording laser light in the C h - B at the polarized lightsplitter varies on the radius direction of the glass master 23 from astate in which the optical axes of the recording laser lights in boththe channels completely coincide. As the exposure spot of the recordinglaser light in the Ch-B moves in the radius direction on the glassmaster 23 by the change in the reflection angle in the same manner as inthe case of the wobbling shown in FIG. 6, the exposure spots in both thechannels are spaced apart.

Next, a track format of the optical disk substrate will be described. Inthe past, "a single spiral structure" forming one-line spiral shapedrecording track T as shown in FIG. 7A has been employed, but, recentlyvarious kinds of formats have newly been proposed in order to aim forhigh density of a recordable optical disk. One of them is a doublespiral structure as shown in FIG. 7B to form 2-line spiral shapedrecording tracks Ta and Tb.

As the double track structure has a fault in that jumping from either ofthe recording tracks Ta or Tb to another must be carried out in order toaccess all of recorded positions on the tracks, it is a format to beemployed in case its merit in improving the record density far outweighsits fault.

There are following two kinds of method to form the double spiralstructure.

As a first method, there is a method in which a feed pitch of theexposure spot at the time of cutting is set twice as many as the trackpitch p to 2p to use both the groove and the land as an record area(called as a land/group record method). Generally, the width of each ofthe groove and the land is set to p each.

The first method effectively makes use of an area which has in the pastbeen used only as a tracking guide groove out of the land and the grooveto improve the record density and is thought to be the most reliablemethod for the high densification of a future optical disk.

As a second method, there is a method in which two spots away by thetrack pitch p in a radius direction are subjected to the exposure andits feed pitch is set two times the track pitch p to 2p at the time ofthe cutting (called "a 2 spot exposure method").

As a representative example for this method, there is "an intermittentwobbling method" which the applicant of the present invention proposes(U.S. patent application Ser. No. 08/823,879). This method is applied bymodifying the form of the wobbling for recording the above-mentionedaddress signal and the like, in which, as shown in FIG. 8, assuming thatone of the tracks T a and T b (T b in the drawing) is made as a wobbletrack, its exposure spot (spot B) is vibrated while in the remainingtrack (T a in the drawing), its exposure spot (spot A) is normally letto advance straightforward.

There is a problem with the normal wobbling in that, as the track pitchis made narrower, leakage (cross talk) record signals between adjoiningtracks becomes larger, thereby making it difficult to read out thesignal correctly. However, according to the intermittent wobblingmethod, because a wobbled track exists only at every other line, it ispossible to sufficiently prevent the cross talk and correctly read out asignal even in a case the track pitch is narrow. This method isscheduled to be employed by the second generation MD-DATA, which is akind of mini-disk.

The 2 spot exposure method is carried out, using by a cutting machinehaving a 2 light optical system as shown in FIG. 5.

By the way, the double spiral structure mentioned above is a trackformat proposed to aim for the high densification of the record area inthe recordable optical disk and presupposes to have only a data recordarea consisting of the groove and the land.

In contrast to this, it is general for optical record media of variouskinds including, for example, an optical disk to beforehand recordinherent information concerning a format, and also, in addition to thebeforehand recorded information of the various kinds, there exists anoptical disk (is called a "partial ROM") in which a user can writeinformation later, but no optical disk with a track format suitable forthese has ever been proposed yet.

SUMMARY OF THE INVENTION

In view of such aspects, it is an object of the present invention topropose a way to beforehand record an inherent information concerning aformat, an optical record media with a track format suited for thepartial ROM, its manufacturing method and the like.

An optical recording medium according to the present invention includestogether a data recording area forming a track of a double spiralstructure consisting of a groove and a land, and a reproduction onlyarea forming a single spiral structure consisting of a pit row.

According to the optical recording medium, as there exists thereproduction only area with the single spiral structure consisting ofthe pit row other than the data recording area, it becomes possible tobeforehand record inherent information concerning a format and otherinformation of various kinds.

A manufacturing method of the optical recording medium is according tothe present invention, in a manufacturing method for an opticalrecording medium comprising; a process for forming photosensitive layeron a master; a cutting process for forming a latent image of a track bysubjecting the photosensitive layer to exposure; a process for forming atrack pattern on the master by developing the photosensitive layer; anda process for molding a substrate of an optical recording medium havingthe same pattern as this pattern, is characterized in that in thecutting process, the latent image of the track having a double spiralstructure in the data recording area is formed by an exposure spot at apredetermined feed pitch while a latent image of a the track in areproduction only area having single spiral structure is formed by anexposure spot at a narrower feed pitch than the predetermined feedpitch.

According to the manufacturing method, because the feed pitch of theexposure spot for forming the latent image the track having singlespiral structure in the reproduction only area is made narrower than thefeed pitch for forming the latent image of the track having the doublespiral structure of the data recording area, the track pitch in thereproduction only area becomes narrower than 2 p (that is, becomesnarrower than twice the track pitch p in the data recording area. As aresult, it becomes possible to manufacture an optical recording mediumwherein the recording densities of the data recording area and thereproduction only area are respectively improved without being subjectedto restrictions by the mutual formats.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 1C are perspective views showing an example of a structureof an optical disk;

FIG. 2 is a diagram showing one example of a process for manufacturing asubstrate of the optical disk;

FIG. 3 is a diagram showing one example of a structure of the cuttingmachine;

FIG. 4 is a block diagram showing one example of an optical system ofthe cutting machine in FIG. 3;

FIG. 5 is a block diagram showing one example of the structure of thecutting machine;

FIG. 6 is a perspective view showing one example of wobbling;

FIGS. 7A and 7B are diagrams showing an example of a track format of aconventional optical disk;

FIG. 8 is a diagram showing one example of intermittent wobbling system;

FIG. 9 is a diagram showing one example of a track format of an opticaldisk according to the present invention;

FIG. 10 is a diagram showing another example of a track format of anoptical disk according to the present invention;

FIG. 11 is a diagram showing a further example of a track format of anoptical disk according to the present invention;

FIG. 12 is a diagram showing one example of the cutting method accordingto the present invention.;

FIG. 13 is a diagram showing another example of the cutting methodaccording to the present invention;

FIG. 14 is a diagram showing another example of the cutting method forproviding a reproduction only area other than a data recording area;

FIG. 15 is a diagram showing another example of the cutting methods forproviding a reproduction only area other than a data recording area;

FIG. 16 is a diagram showing a method for shifting between thereproduction only area and the data recording area; and

FIG. 17 is a block diagram showing an example of a system structure on afeed mechanism control system in the cutting machine according to thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereafter, an embodiment according to the present invention will bedescribed with reference to the accompanying drawings.

FIG. 9 to FIG. 11 respectively show examples of track formats of opticaldisks simultaneously having a data recording area forming a track of adouble spiral structure consisting of a groove and a land, and areproduction only area forming a track of a single spiral structureconsisting of a pit row. As shown in FIGS. 9 to 11, tracks Ta, Tb aregroove-structured tracks, and a land portion is formed between thetracks Ta and Tb. It is possible to employ an optical disk according toanother embodiment allowing land/groove recording in which the track Tais formed of the groove and the track Tb is formed of the land,particularly, in correspondence with the structure shown in FIGS. 5 and7A, 7B.

The following will be reason why the reproduction only area is of asingle spiral structure.

On the premise that continuous exposure (without stopping at any momentthe feed action by a feed mechanism as well as the rotational action bya turn table, and never allowing them to carry out a discontinuousoperation) is carried out like the present cutting method, as a cuttingmethod for providing the reproduction only area other than the datarecording area, the following method will be conceivable.

1 A method to carry out the cutting by one exposure spot in thereproduction only area.

This will be divided into the following 2 ways.

A first method is such one that as shown in FIG. 12, in a case a latentimage of a track having a double spiral structure in a data recordingarea is formed by a land/groove recording method, a spot A, which hasformed a latent image on a groove in a data recording area is used as itis for forming a latent image of a track in a reproduction only area(ROM area).

A second method is such one that as shown in FIG. 13, in a case thelatent image of the track having the double spiral structure in the datarecording area is formed by the 2 spot exposure method, one spot (spot Bin the figure) out of 2 spots A and B is used to form the latent imageof the track in the reproduction only area.

In these methods, the track in the reproduction only area is of a singlespiral structure.

2 A method for carrying out the cutting by 2 exposure spots.

This will be divided into the following 2 ways.

A first method is such one that as shown in FIG. 14, in a case thelatent image of the track having the double spiral composition in thedata recording area is formed by the land/groove recording method,another spot B away in a radius direction from the spot A by a distancep relative to a feed pitch 2 p is added for use in order to form thelatent image of the track in the reproduction only area.

A second method is such that as shown in FIG. 15, in a case the latentimage of the track having the double spiral structure in the datarecording area is formed by the 2 spot exposure method, the spots A, Bare used as they are for forming the latent image of the track in thereproduction only area.

In these methods, the track in the reproduction only area is of thedouble spiral structure.

The fact that the track in the reproduction only area is made of doublespiral structure has a defect in that, as mentioned before, the trackjumping has to be carried out, and further, unlike the data recordingarea, the merit of the improved recording density does not outweigh thedefect in a case of the reproduction only area. Also, other than thedefect, there are other defects; one being that it takes time because arecord signal to the reproduction only area has to be divided into 2signals for 2 exposure spots (that is, for 2 channels) from one master;and the other being that as the 2 exposure spots pass through differentoptical paths in the cutting machine, it is considerably difficult toobtain equal reproduction signals from pit rows exposed to the light bythe exposure spots (the exposure for forming a pit sensitively reflectsthe forms of the spots in a tangent direction to the track when comparedwith the exposure for forming a groove, therefore, its control isdifficult).

Further, as a more serious problem, there is a problem ofinterchangeability with a track format of a reproduction only recordingmedium which a recording and reproduction apparatus of a recordableoptical disk and other optical recording media supports. The trackformat of the reproduction only recording media in such a recording andreproducing apparatus is of single spiral composition and therefore, ifthe reproduction only area is made to be of the double spiral structure,its design becomes burdensome because a counter-measure has to becontemplated how to cope with such problems as the track jumping and thetracking servo in the design of the recording and reproducing apparatus.

On account of such reasons, the reproduction only area is made to be ofthe single spiral structure. As a result, simplification of the systemof the recording and reproducing apparatus, recording work in thereproduction only area and improvement of accuracy of a reproductionsignal from the reproduction only area can be realized.

Next, the disk according to the present invention is, in an opticalrecording medium comprising the data recording area forming the doublespiral structured track consisting of a groove and a lane; and thereproduction only area forming the single spiral structured trackconsisting of a pit row, characterized in that a track pitch in thereproduction only area is narrower than twice a track pitch in the datarecording area.

The following are reasons why the track pitch in the reproduction onlyarea is made narrower than twice the track pitch in the data recordingarea.

When the reproduction only area is made to be of single spiral structureby the above-mentioned first and second methods as shown in FIG. 12 andFIG. 13, the feed pitch becomes 2 p relative to the track pitch p in thedata recording area of the double spiral structure, so the track pitchin the reproduction only area becomes 2 p (that is, twice the trackpitch p in the data recording area). Therefore, the recording density inthe recording only area becomes lower than a technological limit.

If it is only to beforehand record inherent information concerning aformat, such a decrease in the recording density does not pose anyproblem as a recording capacity of the reproduction only area can benegligibly small. But in the case of the partial R O M, a decrease inthe recording density of the reproduction only area is a seriousproblem.

Also, when compared in terms of the same recording density, a recordingsignal to the reproduction only area, is not coincident with a recordingsignal to the data recording area (a phase change signal or amagneto-optical signal) in a signal characteristic (a skew margin andthe like). Therefore, it is unnecessary that the recording density ofthe reproduction only area is made the same as that of the datarecording area. There is no existence of any reason that at least thetrack pitch in the reproduction only area must be two times or larger aswide as that of the data recording area.

On account of such reasons, the track pitch in the reproduction onlyarea is set to being narrower than twice the track pitch in the datarecording area. As a result, it becomes possible to improve therecording densities of both the data recording area and the reproductiononly area without being subjected to restrictions by the mutual formats.

Also, as an example, the track pitch in the reproduction only area ispreferably made to coincide with a track pitch in a track format of areproduction only recording medium supported by a specified driveintended to practically drive an optical recording medium. By so doing,interchangeability with the reproduction only recording medium driven bythat drive can easily be maintained.

Of these, in a case of the above optical disk employing the datarecording area and the reproduction-only area shown in FIG. 9, the datarecording area and the reproduction only area (R O M area) are separatedby an area where a track is not formed (is called a no signal surface ormirror surface).

In an example of FIG. 10, there exists an area where the data recordingarea and the reproduction only area are partially overlapped (the areawherein a track T in the recording only area is sandwiched betweentracks Ta and track Tb in the data recording area).

These track formats are realized by separately cutting the datarecording area and the reproduction only area independently of eachother at the time of cutting.

That is, if a range of a recording radius Rr which the reproduction onlyarea occupies on an optical disk is set to r1≦Rr≦r2 and a range of arecording radius R w which the data recording area occupies is set tor3≦Rw≦r4, in the case of FIG. 9, by setting r2<r3 and in the case ofFIG. 10, by setting r2>r3, the data recording area and the reproductiononly area have to be respectively subjected to the cutting. Here, thelarger an absolute value of a difference between r2 and r3 is (that is,the larger the no signal surface in FIG. 9 and an overlapping area inFIG. 10 are) the more loss of the recording capacity increases, so it isdesirable that the value can be made as near zero as possible. Thisdepends on a positioning accuracy of the exposure spot in a radiusdirection at a starting time and a finishing time of the cutting, but,as a machine of today has a positioning accuracy of up to 5 μm (to anextent of 10 tracks), loss of the recording capacity can be negligiblyreduced.

Meanwhile, in the examples of FIG. 9 and FIG. 10, as the reproductiononly area and the data recording area become perfectly discontinuous,even if a track in one area of the reproduction only area and the datarecording area is followed directly a shift to a track in another areais not presented. Then, in order to reproduce recording signals of thewhole areas from an optical disk having such a track format, there is aneed for a method which makes possible the shift between thereproduction only area and the data recording area.

As to this method, for example, a method currently practiced for theshift between the reproduction only area and the data recording area ina recordable mini-disk is preferably used.

FIG. 16 is a drawing showing this method. First of all, several tracksin the neighborhood of a boundary between the reproduction only area andthe data recording area are set to an area which is not used forrecording and reproducing (referred to as a shift area or non-use area).Then, as indicated as 1 in the same drawing, for example, at the timewhen the reproduction of a recording signal in the reproduction onlyarea is finished, a reproduction spot is made to jump across the shiftarea to an appropriate position in the data recording area. At thistime, a gain (depending on a case, polarity, too) of a tracking servosystem is changed over between the reproduction only area and the datarecording area. Next, as indicated as 2 in the same drawing, based on anaddress signal (address information inserted by address bit or wobbling)of a track in the data recording area on which the reproduction spot haslanded, a target address is searched for.

In order for an optical disk with a track format in FIG. 9 and FIG. 10to utilize this method, it is enough that, an area equivalent to thesumming of several tracks in front and in the rear of each of ano-signal surface in FIG. 9 and an overlapping area in FIG. 10 is set tothe shift area.

Next, in an example of a format in FIG. 11, one track (here, Ta) out oftracks Ta and Tb in the data recording area is contiguous with a track Tin the reproduction only area.

This track format can be realized, at a time of cutting, by changing afeed pitch of an exposure spot at a boundary portion between a part toform a latent image of a track in the data recording area and a part toform a latent image of a track in the above-mentioned reproduction onlyarea.

That is, for example, in a case when a track pitch in the reproductiononly area is set to 0.9 μm and a track pitch in the data recording areais set to 0.9 μm by adopting the land/groove recording method, first ofall, after finishing the cutting at a feed pitch of 0.9 μm in thereproduction only area, the feed pitch is changed up to 1.8 μm, whilethe exposure spot is moving in the boundary portion (a shift area inFIG. 7) toward the data recording area.

Also, for example, in a case when the track pitch in the reproductiononly area is set to 0.9 μm and the track pitch in the data recordingarea is set to 0.9 μm by adopting the 2 spots exposure method,, first ofall, after finishing cutting at a feed pitch of 0.9 μm in thereproduction only area, the feed pitch is changed up to 1.8 μm, whilethe exposure spot is moving in the boundary part toward the datarecording area and when the exposure spot reaches the data recordingarea, another exposure spot is added apart by 0.9 μm away in a radiusdirection from the exposure spot. In the 2 examples mentioned above, itis also a matter of course that the feed pitch is preferably changed to0.9 μm while the exposure spot is moving in the boundary portion towardthe reproduction only area after the cutting is first of all finished ata feed pitch of 1.8 μm in the data recording area.

By the way, if the feed pitch is changed during the cutting, itnaturally takes a little time before the feed pitch becomes stabilized.The feed mechanism of the present cutting machine employs an air slidemethod by a linear motor or an air static pressure screw method. In theair slide method, a result of an actual measurement of a required timewas about 1/15 sec. Therefore, if a number of revolution of a turntableof the cutting machine is set to 900 revolutions per minute (15revolutions per minute), it is possible to stabilize the feed pitch atthe changed pitch while the turntable revolves almost once. Therevolution number of the turntable in the present cutting machine is, ingeneral, in a range of 200˜250 revolutions per minute, and therefore, asit is possible to stabilize the feed pitch while the turntable revolvesthree times at the maximum, it can be said that practically there is noproblem.

Meanwhile, in a case of reproducing a record signal from the opticaldisk with a track format in FIG. 11, it is appropriate to let theexposure spot jump the track, as in FIG. 16, in the shift area betweenthe reproduction only area and the data recording area. Its reason isthat, first of all, the gain of the tracking servo system (depending ona case, even the polarity) can be changed over while carrying out thetrack jumping. Also, secondly, although there is a case wherein a signalis recorded first on the land in the land/groove recording methodbecause it is possible to first shift to the land in the data recordingarea is followed as it is, by jumping the tracks, whereas if the trackin the reproduction only area is followed as it is, the shift to thegroove in the data recording area occurs,.

There are following advantages with the track format in FIG. 11 ascompared with the track formats in FIG. 9 and FIG. 10.

(a) Even in a case of having landed by mistake on the shift area at atime of jumping the tracks, because there exists a groove in the shiftarea, it is possible to continuously shift to the groove in the datarecording area as it is. Therefore, there is few risk for the exposurespot to move recklessly.

(b) As mentioned above, because the feed pitch after it was changed canbe stabilized while the turntable revolves three times at the maximum,the width of the shift area can be made narrower than the cases in FIG.9 and FIG. 10. As a result, the probability that the exposure spoterroneously lands on the shift area is made low.

By the way, a control system of the feed mechanism of the currentcutting machine has, as an example, a following systematic structure. asshown in FIG. 17.

(1) Either of information of the recording linear velocity (CLV) or anumber of revolution of the turntable (CAV), and information on the feedpitch are given to a system controller SC (in a case when theinformation on the C L V has been given, information on a recordingradius is also given to the system controller) to let it calculate afeed speed of the feed mechanism from the informations.

(2) This feed speed information is given to a digital signal processorDSP to let it produce digital data of a predetermined bit (for example,24 bits). By increasing the number of the bit, the feed speed can be setfinely. Also, when the feed speed is calculated by using the CLVinformation and the recording radius information, the feed speed variesdepending on the recording radius, but, even in the case, by increasingthe number of the bit it becomes possible to control the feed speed inhigh precision.

(3) The digital data is given to a direct digital synthesizer to convertthe data to a pulse signal of a frequency depending on the feed speed.

(4) The pulse signal is given to a feed mechanism driver D R to activatethe feed mechanism (a motor and the like) at a feed speed correspondingto the frequency of the pulse signal.

Then, in order to change the feed pitch while the cutting is beingcarried out, as shown in FIG. 17, there should preferably be a systemstructure in which a program is so incorporated that, in a stage of theabove-mentioned (1), a plurality of feed pitch informations and aplurality of corresponding recording radius information are given to asystem controller S C.

Alternatively, in cases wherein it is possible for a change in the feedpitch p to be limited to numbers which are power times as large as two(2p, 4p, . . . ) or numbers which are inverse number times of powertimes as large as two (p/2, p/4, . . . ), at the above-mentioned stage(3), as shown in FIG. 17, after firstly generating a high frequencypulse signal with a frequency f in order to improve resolution,frequency-dividing the same to generate pulse signals of frequenciesf/2, f/4, f/8, f/16 and so on, the pulse signals to be supplied to adriver D R can preferably be changed over in accordance with therecording radius by supplying these signals to a selector SL as well asletting selection by the selector SL change over depending on therecording radius. In FIG. 17, such a state is shown in which at presenta pulse signal with a frequency f/4 is supplied to the driver DR and asignal is supplied to the selector SL for changing over its selection toa pulse signal with the frequency f/8.

Further, in the above embodiments, the present invention is applied tothe optical disk, but it is preferably applied to other opticalrecording media (for example, an optical card and the like).

Also, the present invention is not limited to the embodiments mentionedso far, but as a matter of course, can employ various other structureswithout departing from the spirit or scope of the present invention.

As mentioned so far, according to the present invention, as there existsthe reproduction only area forming the single structured trackconsisting of pit rows other than the data recording area the formingdouble spiral structured track consisting of the groove and the land, itbecomes possible to beforehand record the inherent information on theformat and other various kinds of information in the reproduction onlyarea.

Also, in a case wherein the track pitch in the reproduction only area ismade to be narrower than two times the track pitch in the data recordingarea, i.e., the feed pitch of the exposure spot at a time of forming thelatent image of the single spiral track in the reproduction only area ismade to be narrower than the feed pitch to form the latent image of thedouble spiral track in the data recording area, it becomes possible torespectively improve the recording densities of the data recording areaas well as the reproduction only area without being subjected torestrictions by mutual formats and The an interchangeability with thereproduction only recording media is presented.

Having described preferred embodiments of the present invention withreference to the accompanying drawings, it is to be understood that thepresent invention is not limited to the above-mentioned embodiments andthat various changes and modifications can be effected therein by oneskilled in the art without departing from the spirit or scope of thepresent invention as defined in the appended claims.

What is claimed is:
 1. An optical recording medium comprising;a datarecording area forming a double spiral structured track having spiralrecording tracks each formed of a groove and a land adjacent to saidgroove; and a reproduction only area forming a single spiral structuredtrack consisting of a pit row.
 2. An optical recording medium accordingto claim 1, wherein a track pitch in said reproduction only area isnarrower than two times a track pitch in said data recording area.
 3. Anoptical recording medium according to claim 1, wherein said datarecording area and said reproduction only area are spaced away by anarea wherein a track is not formed.
 4. An optical recording mediumaccording to claim 1, wherein said data recording area and saidreproduction only area are partially overlapped.
 5. An optical recordingmedium according to claim 1, wherein one track in said data recordingarea is contiguous with a track in said reproduction only area.
 6. Anoptical recording medium comprising;a data recording area forming adouble spiral structured track having two spiral recordable tracks byalternately arranging a groove and a land; and a reproduction only areaforming a single spiral structured track consisting of a pit row.
 7. Anoptical recording medium according to claim 6, wherein a track pitch insaid reproduction only area is narrower than two times a track pitch insaid data recording area.
 8. An optical recording medium according toclaim 6, wherein said data recording area and said reproduction onlyarea are spaced away by an area wherein a track is not formed.
 9. Anoptical recording medium according to claim 6, wherein said datarecording area and said reproduction only area are partially overlapped.10. An optical recording medium according to claim 6, wherein one trackin said data recording area is contiguous with a track in saidreproduction only area.